氨-煤在沉降炉中掺烧试验及氨的氧化动力学

Experiment of ammonia-coal co-firing in a drop tube furnace and thekinetic modeling of ammonia oxidation

发展先进的碳减排技术、实现双碳目标已成为能源领域最迫切的攻关难题。我国燃煤电厂碳排放占比很大。氨作为零碳燃料,在热值、合成、运输等方面具有显著优势。氨在燃煤锅炉中混烧是实现大规模利用的重要途径,然而大规模掺烧过程中NO_(x)排放控制将是未来面临的主要挑战之一。在沉降炉试验平台对氨煤开展混燃试验,研究温度(1000~1300℃)、空燃比(0.8~1.5)、掺烧比例(0~30%)等对NO_(x)排放的影响。结果表明,控制较低燃烧温度和空燃比是抑制氨向NO_(x)转化的关键。在空燃比1.5、掺烧20%氨工况下,1200和1300℃下NO_(x)排放量可达780×10^(-6)和1870×10^(-6)。随氨掺烧比例增加,NO_(x)排放水平线性增长,但整体燃料氮向NO的转化显著下降。借助详细化学反应机理(Glarborg 2018、Mendiara 2009、Konnov)计算结果表明,Konnov机理预测结果更接近试验结果。进一步采用Konnov机理讨论了燃烧温度、空燃比等变量对纯氨燃烧NO_(x)排放的影响,发现温度与NO_(x)排放浓度呈指数型增长,而空燃比由1.0提高至1.1时NO_(x)排放总量发生突变。引入混合因子讨论氧化剂与氨的混合水平对NO_(x)排放的影响,发现延长氨与氧化剂的混合距离能显著降低NO_(x)排放强度。

At present,the development of advanced carbon emission reduction technologies and the realization of the dual-carbon goals have become the most urgent problems in the energy field.Carbon emissions from coal-fired power plants in China still account for a major proportion.Ammonia,as a zero-carbon fuel,has significant advantages in heating value,synthesis,transportation and other aspects.Co-firing ammonia in coal-fired boilers is one of the important ways to achieve large-scale utilization,however,the control of nitrogen oxide emissions during large-scale co-firing will be a major challenge in the future.In this paper,the co-firing experiment of ammonia with coal was carried out in a lab-scale furnace,and the effects of temperature(1000-1300℃),air/fuel ratio(0.65-1.50),and co-firing ratio(0-30%)on nitrogen oxide emissions were discussed.The results show that the lower combustion temperature and air/fuel ratio is essential to inhibit the conversion of ammonia to nitrogen oxides.Under the operating conditions of 1.5 air/fuel ratio and 20%co-firing ratio,the NO_(x)emissions reach to 780×10^(-6)and 1870×10^(-6)at 1200 and 1300℃respectively.With the increase of ammonia ratio,the NO_(x)emissionsincrease linearly,but the overall conversion of fuel nitrogen to NO decreases significantly.The calculations by detailed chemical reaction mechanisms(e.g.Glarborg 2018,Mendiara 2009,Konnov)show that the prediction results derived by Konnov mechanism are closer to the experimental results.The Konnov mechanism is further used to evaluate the influence of air/fuel ratio,temperature and other variables on the NO emissions by ammonia combustion.The results show that the temperature and nitrogen oxide emission concentrations increase with exponential rate,while the total NO_(x)emissions change abruptly when the air/fuel ratio increases from 1.0 to 1.1.A mixing factor is defined to study the effect of the mixing level of oxidant and ammonia on nitrogen oxide emissions,and it is found that prolonging the mixing distance of ammonia and oxidant can significantly reduce the intensity of nitrogen oxide emissions.